The SRD only gives a means to determine costs and weights of weapons for Large and Small versions based on the Medium weapons. Any other supplied values are the author's best determination.

A heavy, high caliber, single shot, breach loading rifle. It fires special Alchemical rounds that have varying effects. you may aim and fire with one hand with a penalty of -4 if STR and DEX is 16 or above. Otherwise, take an additional -2 penalty for every two points below 16 your STR or DEX happens to be, whichever is larger. You cannot fire this weapon one handed if you do not have a STR and DEX of at least 10. If gun is being wielded with two hands required STR is 8. If STR is still below that, take a -2 penalty when firing. Change by +/-3 for every size category above and below medium. The Alchemist's Breachload Pistol must be reloaded with two hands. This takes a move action which provokes an attack of opportunity.